Rate of climb indicator



Dec. 25, 1956 R. SALLE ET A1. 2,775,123

RATE OF CLIMB INDICATOR Filed July 29, 1953 comparatively long duration.

United States Patent RATE or CLIMB DIDICATOR.

Ren Salle, Marly le Roi, Paul Etienne Svin, Clamart, and Jean Olivier Mottais, St. Nazaire, France, assignors to Societe Nationale de Constructions Aeronautiques du Sud-Ouest (S. N. C. A. S. 0.), Paris, France, a company of France 2 Application July 29, 1953, Serial No. 371,004

Claims priority, application France August 1, 1952 3 Claims. (Cl. 73-179) being well understood that the invention is in no way limited to the use of said device as a metering apparatus, the above-mentioned movable member being easily adapted to be used, e. g. for controlling, regulating, switching functions or the like.

It may be noted also that a particularly interesting scope of application of said devices is the measure of the rate of climb of aerodynes, the control of the inner pressure of a cockpit or pressurization, the guiding in altitude of airplanes, etc.

The invention relates more particularly to variometers of the type comprising a closed vessel communicating through a capillary tube with an outer space and a differential pressure-responsive device, such as an aneroid diaphragm-case having its inner space in permanent communication with said vessel and its outer wall exposed to the pressure in said outer space, the deformation of said diaphram-case being used to position the index of the variometer.

The operation of such a variometer is based on the fact that when the pressure in the outer space is varied, the pressure in the vessel also undergoes a variation but always with a certain pressure difference due to the loss of pressure through the capillary tube. This is illustrated in Fig. 4 of the accompanying drawings which shows variations of pressure versus time. Let it be pointed out that these curves are purely explanatory and do not pretend to any mathematical accuracy. In this diagram, curve V1 shows an example of a pressure variation in the closed vessel of a variometer, in response to a variation V2 of the outer pressure.

Now, when V2 varies at a constant rate, the pressure difference 2 between V2 and V1 also remains substantially constant, so that the position of the index of the variometer which is determined by the deformation of the diaphragm-case, that is in turn a function of the value of the shifting or pressure difference 6, gives an indication of said rate of variation.

Unfortunately, as shown in the diagram, the difference between pressures V1 and V2 assumes only its steady value e, at a certain time t1 after the origin to of the variation of the outer pressure V2, so that a correct indication of the rate of variation V2 is obtained only at the end of a transient period tut1 which is often of This is due to a number of phenomena inherent with the very nature of such a variometer.

First of all, a certain time is required for buildingup through the capillary tube from pressure equilibrium the constant rate of flow corresponding to the steady 2 value e of the pressure shifting. This inertia of the capillary tube depends upon the length. and cross-section of the capillary tube. A second type of phenomena which extends the duration of the transient period is due to temperature influences, such as the cooling eifect due to the expansion of air in the closed vessel.

The inertia of the capillary tube may he obviously partially disposed of by reducing its length and/or increasing its cross-section. This is the solution which has been adopted in aircraft panel-variometers. However, it offers the drawback of reducing the value of the pressure differential for agiven rate of variation of the outer pressure and, hence, the power available at the index, which is objectionable in controlling applications such as pressurization.

In order to attenuate the influence of the thermal phenomena, there have been proposed heretofore, a number of insulating arrangements such as the so-called Dewar flask. These devices, however, have the drawback of being exceedingly fragile, complicated and expensive.

The invention has for its purpose to reduce the transient period of a variometer by extremely simple means and hence at a very low cost without decreasing, and even while permitting a considerable increase of, the pressure difference and, hence, the actuating power available at the index.

With this purpose in view, the invention has for its main object to provide a variometer of the type described including movable control means to vary the capacity of its closed vessel, and locating means to hold said movable control means stationary when they are not operated. This arrangement permits, by operating said capacity varying means immediately prior to the use of the variometer, creating artifically a pressure ditference to thereby reduce the transient period required for the establishment of the pressure difference in operation. It only implies that the expected variation is known, at least approximately.

Now, it is obvious that if the rate of variation of the outer pressure is more accurately known before hand, which is the case, e. g. when the variometer is intended to check the known rate of climb of an airplane or to control pressurization during a descent or a climb at a known rate, it will be possible to predetermine the optimum extent to which the capacity of the vessel is to'be varied to reduce the duration of the transient period to a minimum.

Experiments have shown that the optimum value of the pressure variation to be imparted to the vessel of the variometer before use, is substantially equal to one and one-half times the expected pressure difference.

A more particular object of the invention is therefore to provide a variometer with variable capacity of the type described, further comprising means to control the extent to which its capacity is varied, said means preferablyincluding an indicator associated with a scale graduated in terms of the rate of variation of the outer pressure.

In the diagramof Fig. 4, it may be seen easily that if the initial value of the pressure in the closed vessel is brought to P1, instead of Po, the transient period is reduced to tu-t2, instead of to-ti.

A further advantage of the variometer according to the invention, is that the pressure difierence may be considerably increased without increasing the duration of the transient period. This is illustrated in the dotted curve V3 plotted in Fig. 4, which clearly shows that if the length of the capillary tube is so increased as to obtain a shifting e1 consideraby greater than c, all other things being equal, it is possible to maintain the same duration to-t2 of the transient period instead of tn-ts, by initially varying the-capacity 9t the vessel to such an extent as to build-up in said vessel a suitable initial pressure P2.

This advantage is particularly interesting in pressuriza- ,-.,.gtion, applicationsgwhere, the;,index is vadvent,ageously caralilev of physical controlling .powen To illustrate .the oss ibilities of Va -;variometer, according to, .the invention, t will-be pointedout-thah, all other things being equal, it ,ermits, tonexample, of proyiding apressure difference of 10 g./cm.?.instead of 1. g./cm. .with .a similar con- -,=3aventionalwariometer.].Similarly,-to give-anidea of the .;g cons iderablereduction ofthe present period that may be obtainedz tcqs ording tothe invention,-eXper-irnents have hown;that,;for a rateof climb of 3 m./sec., a convenional variomete1 of lglitre capacity: equipped ,with a 30 m -long,capillarytube hasi a transient period of about minutes,-whiclrmay-be reducedas far as to 15 seconds the'samevariometeris provided with avessel having a variable capacity. As a comparison, letzit be added that f -ifi, ,the same- .were.,provided with .a; Dewar. flask of first 'graclc it would still req uire aboutlminute to reach its ,.steady rate o operation.

Other objects and advantages of the invention will be apparent\from the following detailed description, together with the accompanying drawings, submitted for ,;,;-purposes of illustration only and notintended to define ,;-.th e scope ofi-the invention, reference being had for that -purpose tothe subjoined claims.

In these drawings: ,QFigs. 1-to3 are diagrammatic sectional views of three embodiments of variometers according to theinvention. closed vessel 1 communicates with arr outer space only through a: capillary tube 2. ,An'aneroid diaphragmcase-3,-the, deformation of which detects the. pressure difterence betweentheinner space of the vessel 1 and the omen-space has its outer'wall. exposed to the pressure in qsaidvoutergspace and its inner.space-communicating with g-vessel 1. V

,Fig. '1, shows a variometer in which the diaphragmcase 3 ispperatively connected with an index 4 cooperating' witha graduated scale 5. The position of index 4 indicates the rate-of variation of the pressure in the outer space e. g. corresponding to the rate of climb or descent-- ofan aerodyne.

, wln the alternativeembodirnent shown inFigs. 2 and 3, ,diaphragm-case 3 is supposed to be operativelyconnected 1 With any movable element foreffecting any suitable cont trol 'lingoperation, such as pressurization. In.-the:eXample shown in Fig. 1, the variation of the capacityoflvessell is obtained bytmeans of a piston 6 provided with flpacking rings 7,- said piston which is 0perable'from outside by means of a rod 8, can be located inany selected. position by means of -a set-screw 9. An indicator, 20wfast with ,rod;8, indicates on a scale 21 the pos ition of piston 6. I

In,the=embodiment shown in Fig. 2, the bottom of ves- .;sel,1 contains a liquid-10 the. level ofwhich can be varied by meansof aIpiston'll slidably mounted ina cylinder .12, A locating iinger 13 which, in the example shown, s'subjccted tothe, action (of a spring, permits holding pish in'ga ny selected; position by engagement of said fingerj l3 iinnone of the locatingnetchesv ldprovided, for t his purpose, on the rod of the piston 11.

. Inithe, alternative embodiment shown in ,Fig; 3, the ,,variation ofthe capacity of vessel 1 is obtaine'd by means of bellows 15, the deformation ofwhich can be adjusted -by, means of a ,control-rod, 16 provided with a handle. 3. Saidrodisfurther, provided with two locating notches 17,

,, cooperating with spring-fingers 19.

Injth case of Figs. 1 and 2','the amplitude'of the vol- I iationinaybe'selected according to the expected ate fva'ri'ation o fthe external pressure; In"the ;case of i3,f,said,rate ofvariationhasbeerifasSurned to be conta'ntfand, with the arrangement "shown, it is possible to erminedsxtent.

nc'rease'or deerease the capacity"of vessel l by a prede I The movable control meansof the variometer are so adjusted, as to give the possibility to the operatorusing the said control means to reduce considerably the transient period which appears in these types of variometers 5 between the beginning ofthe variation of the outer pressure and the time whe"1'1"the variometer gives a steady indication. i The variometer according .to the inventionoperates. as Cfc'illows:

. "Afsalready mentioned, the operator islsupposed itojknow at leastoapproximately the rate-obpressure variation to which the variometer is to be subjected., According as to whether this variation is to be positive or negative, he has' only to depress orcompress,"immediately before the 5 beginning ofithese expected variationsetheinner,space of vessel 1 by acting in the relevant direction upon the handcontrol actuatingthe capacity varyin-g means. If said hand-control is provided with an indicator such as 20 in 1Fig. ;1, -the operator will bring said indicator on; 'a. g'radu- 0;Zation corresponding 1 to, the; expectedg j rate of1--variation, nvlwhereupon hex-Will fix,,:the'amovable member, e. g:' by -means ofs-screw 9t; In the embodimentsrshown in-Figs. 2-,'--and 3, saidalocation;takesiplace automatically; *It is #3180 po'ssible,-within;thescope of the invention, to'provide 5 two-graduated scales for-climb anddescent'respectively or a dilferential--: s'caleto avoid re-setting. ibetween two-suc- 1cessive-operations.

- It is -to be:understood that-theinvention is not limited tQgihCiEXfiHlPlfiSg described and shown and that'itmay be 0 effected with numerous:modifications'withinrither reach ofrthose skilled -inthe ":art without departing ,from the =2 spirit'ofi the invention.

- What I claim is: l 1. A' variorneten-:comprising, lIl'fiOl'l'lbll'lElllOll,,flzClQSBd 5 vessel, a capillary tube connecting ,said,closed-vessel with an' outer space: to vary-the1pressure in s'aid ve'sse1 in re- Q sponse to -pressure "variations in: said ,outer :space with a ,-pres,sure;dil-ference with respect thereto, a device; respon- ,sive'to said pressureadiiference, said-device:having anelel) ment exposed to the pressure in said vessel-and anjeleh ment exposed to the pressure in said outer -,space ,-an-index 1 operatively. -.connected; with said pressure: difference responsive device todetectthe:value of said-pressure. difference and hence the rate of variation of-saidouter 1 space ,pressure; a cylindrical chamber adapted to form part of said vessel,-,mov'able control means within said :chamber to vary-the capacity of said-vessel, locating means to hold: said, movable; control means, stationary when they I are :not operated;sand indicator means to indicate the 1 located position of said. movable control means, whereby the initial pressure in said 'vesseLcan be brought before use -to-aipredetermined value: capable of reducing to a -minimurn wthe. time required for building-up, said Pressure foifference.

2. A -variometeras-.- claimed in claim -1, wherein said pressure difference; responsive device is constituted by. an aneroid diaphragm casehaving its inner space permanent- 'ly. c omrnunieating with said vessel and its outerwall ex- 7 posed to the pressure in said outer space.

3. A variometer acclaimed in claim 1, in whichlsaid .movable control means is a-piston and piston-rod and said-locating means comprises a set screwadapted-to clamp said piston rod at will in anydesired position. 

